1. Field of the Invention
The present invention relates generally to a display apparatus for an automotive vehicle and more specifically to a display apparatus for displaying vehicle-related information to a driver as virtual images by means of a projector and a reflector.
2. Description of the Prior Art
With increasing diversification of display units mounted in automotive vehicles, apparatuses including a projector have recently been proposed as novel display apparatuses for automotive vehicles. FIG. 1(A) shows an example of such a prior-art display apparatus. In the drawing, a projector 4 including a display unit 2 and a lens 3 is arranged within a dashboard 1 so that the optical axis thereof is directed in the upward direction. Further, a half mirror 6 is mounted on the dashboard 1 inside a front windshield 5 with an inclination angle .theta. with respect to a transparent plate (e.g. glass) 1a placed on the dashboard 1.
In the display apparatus shown in FIG. 1(A), a display image from the display unit 2 is projected upon the half mirror 6 through the transparent plate 1a and then reflected by the reflector 6 toward driver 7. Therefore, the driver 7 can see the display images from the display unit 2 as a virtual image 8 outside the front windshield 5, while looking through the front windshield 5 to the outside.
In the above-mentioned prior-art display apparatus, since a half mirror is used, the light availability and image recognizability are not satisfactory.
Further, since the projector 4 is housed in the dashboard 1 together with various instruments, it is very difficult to appropriately arrange the projector 4 within the dashboard 1, and the size and position of the half mirror 6 are restricted in relation to the projector position. Moreover, when the display comprises a liquid crystal display and a light source, it is not easy to effectively radiate heat generated from the light source toward the outside of the dashboard 1.
In addition, in the case where intense sunlight is allowed to be incident upon the transparent plate 1a through the half mirror 6, and then reflected from the half mirror 6 toward the driver 7, as shown in FIG. 1(B), the driver 7 will be unable to clearly recognize the display images of the projector 4.
Furthermore, there exists another problem in that it is difficult to clean the inner surface of the front windshield 5 because the half mirror 6 is mounted on the dashboard 1.
FIG. 2 shows another example of a prior-art display apparatus including a projector. In this example, a projector 13 including a display unit 13a (e.g. liquid crystal display, electron-ray indicator tubes, etc.) is disposed under the meter hood 12 of an instrument panel 11; and a half mirror 14 with a high reflectivity (e.g. acrylic resin or glass whose surface is coated with a metallic film deposition is disposed at an indicator display position within the instrument panel 11, in order to reflect display images 13b projected from the display unit 13a toward the driver 7.
Unfortunately, in this prior-art display apparatus, since the projector 13 is disposed near the half mirror 14, the virtual images are displayed in a relatively short distance corresponding to that between the projector 13 and the half mirror 14, so that the visual recognizability of display image is relatively poor.